1. Field of the Invention
The invention relates to a switched capacitor network having a capacitor being charged and discharged in alternation by a switch device and being connected to a voltage source for charging.
Active networks, to be realized, typically require an operational amplifier as an active component and capacitors and resistors as passive elements. The frequency dependency of the network is determined by the capacitors and resistors being used. Conversely, in switched capacitor networks, resistors are simulated by switched capacitors, and there is a linear relationship between the switching frequency and the equivalent electric conductance or guide value, corresponding to an ohmic resistor. The frequency dependency of the network can thus be varied in a simple way by varying the switch frequency.
As is described in the book entitled: Halbleiter-Schaltungstechnik [Semiconductor Circuitry], by U. Tietze and C. Schenk, 9th Edition, 1991, page 450 ff., the capacitors of a switched capacitor network are switched in such a way that they are each charged in a switching phase and discharged again in an ensuing switching phase. Instead of the discharge, a charge reversal can also ensue, which is equivalent to discharging with subsequent charging having opposite polarity. The onset of the charging or charge reversal process represents a major load for the charging voltage source, since the capacitor briefly forms a short circuit, and the current is primarily limited only by the internal resistance of the voltage source and the contact resistance of the switch device. The consequence is initially a voltage dip at the voltage source and subsequently a transient effect, which is determined essentially by the capacitance of the capacitor, the internal resistance of the voltage source, and the contact resistance of the switch device. That can cause inadequate charging of the respective capacitor in the corresponding switching phase, and resultant disruptions in the entire network.